1. Field of the Invention
This invention relates to high-resolution display apparatus utilizing a cathode ray tube (CRT) for presenting color graphics. More particularly, this invention relates to such apparatus wherein the CRT control data is stored in digital format and is converted to analog format for controlling the CRT electron beam guns.
2. Description of the Prior Art
Systems for producing high-resolution displays on CRTs, such as for computer graphics displays, commonly develop the picture control data in digital format. Such data is stored in a so-called frame buffer comprising a large number of random-access-memory devices (Video RAMs) arranged as storage banks for the CRT pixel signals. The frame buffer conventionally is controlled by a graphics processor which directs the transfer of data to and from the frame buffer in properly synchronized fashion. The digital data read-out from the frame buffer is directed to a set of digital-to-analog converters which produce corresponding analog signals for respective color guns of the CRT, thereby to control the intensity of each color (red, green, blue) for each pixel of the CRT display. For these various data transfer and other operations, precisely-controlled timing signals are required.
Prior art system arrangements and integrated-circuit devices used therewith have been ill-suited to obtain optimum operation, and particularly have been unable to provide flexibility for adapting to different operating modes as desired by manufacturers of different types of graphic display apparatus. For example, the graphics processor and frame buffer commonly have been interconnected through specialized logic circuits which are not readily alterable to meet different operating conditions. Thus each system must in effect be custom crafted for its particular application. In addition, prior art systems typically have required the use of fast TTL logic circuitry (dividers, flip/flops and gates) which can create problems through generation of electromagnetic radiation.